1. Field
The exemplary embodiments relate to a method of outputting an audio signal and an audio signal output apparatus using the method, and more particularly, to a method of outputting an audio signal and an audio signal output apparatus using the method to improve sound quality of an audio signal and decrease noise and errors that may occur during a switching amplification operation.
2. Description of the Related Art
Examples of an audio power amplifier capable of receiving an audio signal and then outputting an acoustically-recognizable signal include a class-A amplifier, a class-B amplifier, a class-AB amplifier, and a class-D amplifier. Among these examples, the class-D amplifier is widely used because it can reduce a drop-off in amplification efficiency which may occur in the class-A amplifier, the class-B amplifier, the class-AB amplifier, and the like.
The class-D amplifier is a digital amplifier that modulates an analog audio signal into a digital audio signal, performs signal processing such as noise removal on the digitally-modulated audio signal, and amplifies the digitally-modulated audio signal. The digitally-modulated audio signal is amplified to a signal having a high voltage level. Here, the amplification is achieved using a switching amplifier, which receives power having a high voltage level and power having a low voltage level. Afterwards, the switching amplifier performs a switching operation according to an input digital signal, thereby outputting audio signals having a logic-high voltage level and a logic-low voltage level.
Although the digital amplifier has a high amplification efficiency, sound quality of the output audio signal is not smooth and tends to have a monotonous tone. Also, due to harmonic components which may occur in the digital amplifier, a negative distortion of sound may occur.
Also, when the switching operation is performed by the switching amplifier, switching noise occurs. The switching noise decreases a signal-to-noise ratio (SNR) of the switching amplifier. Power noise such as a ripple exists in power that is supplied to the switching amplifier. The power noise also decreases the SNR. In addition, a switching loss, falling of a switching driving signal, and a delay of a rising time, which occur during a switching amplification operation, cause a non-linear characteristic of the output audio signal.
Thus, a method and apparatus capable of addressing the problems of the digital amplifier, which are a monotonous tone, a decrease in the SNR, and non-linearity, is required.